Danny Rowe's spot-kick four minutes before half-time and a second 16 minutes after the break put the Coasters well on their way and substitute Matt Hughes added their third with 16 minutes to play.
United had more than held their own during the first half, but never seriously looked like getting back into contention once the eventual champions went in front.
It was the visitors who edged in front in the 41st minute following a tight first half in the April sunshine.
Kalern Thomas got the wrong side of Brendon Daniels and hauled him to the ground and once referee Declan Bourne had pointed to the spot, ROWE confidently drove home the penalty despite Ross Durrant guessing correctly.
Daniels sailed an effort marginally wide at the beginning of the second half but Fylde were two goals to the good on 61 minutes when ROWE had the freedom of the United half to pick his spot beyond Durrant.
United sub Liam Adams was denied by visiting keeper Rhys Taylor before Fylde sealed the match and the title with a well-taken third.
Matt Blinkhorn cut the ball back from the right and HUGHES steered home from inside the penalty area to start the promotion party.
Mani Dieseruvwe was denied by a terrific Josh Langley block in the closing stages, while Jay Rollins planted a free header over the bar following Adams’ cross.
Boston (4-2-3-1): Ross Durrant; Kalern Thomas, Tom Batchelor, Nat Brown, Jan Yeomans; Adam Chapman, Jack Broadhead; Louis Briscoe (Liam Adams 67), Lewis Hilliard (Karl Hawley 68), Jay Rollins; Mani Dieseruvwe (Colby Bishop 79). Subs (not used): Harry Vince, Charlie Gatter.
AFC Fylde (4-2-3-1): Rhys Taylor; Caspar Hughes (Richie Baker 81), Josh Langley, Dom Collins, Tom Kennedy; David Morgan, Andy Bond; Matt Blinkhorn, Dan Bradley (Bohan Dixon 31), Brendon Daniels (Matt Hughes 59); Danny Rowe. Subs (not used): Kieran Kennedy, Tony Thompson (gk).
Referee: Declan Bourne.
Attendance: 1,255 (128 visitors).